The expression of granulocyte macrophage-stimulating factor (GM-CSF) and GM-CSF receptors in the human endometrium suggests an autocrine/paracrine role for GM-CSF in this tissue. Using primary cultures of isolated endometrial glandular epithelial and stromal cells, the present study examined: (i) the cell specific expression of GM-CSF and GM-CSF receptor mRNA and protein; (ii) direct action of GM-CSF on the rate of DNA synthesis and cell proliferation; and (iii) regulation of GM-CSF expression through its interaction with transforming growth factor (TGF)-beta1 in these cells. Quantitative reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay and immunocytochemistry indicates that glandular epithelial and stromal cells express GM-CSF, GM-CSF alpha and GM-CSF beta receptor mRNA and protein. The epithelial cells express a significantly higher level of GM-CSF mRNA than stromal cells while both types produce low concentrations of protein. At 0.01-100 ng/ml GM-CSF did not have a significant effect on the rate of [3H]-thymidine incorporation or proliferation of epithelial and stromal cells. However, GM-CSF (1 ng/ ml) up-regulates its own protein expression, but does not effect TGF-beta1 mRNA protein expression in epithelial and stromal cells, and actually inhibits the cell-associated TGF-beta1 protein in stromal cells (P<0.05). At 1 ng/ ml TGF-beta1 up-regulates its own mRNA and protein expression in epithelial and stromal cells (P<0.05), with no significant effect on GM-CSF expression. Co-treatment of the cells with GM-CSF + TGF-beta1 resulted in an increased production of GM-CSF protein as well as TGF-beta1 mRNA and protein expression by epithelial and stromal cells, compared with untreated controls (P<0,001). In conclusion, the results suggest that GM-CSF is not a mitogenic factor for endometrial glandular epithelial and stromal cells, however, in an interactive manner with TGF-beta1 it regulates its own and the expression of TGF-beta1.